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Abstract:

Double core-shell fluorescent materials and preparation methods thereof
are provided. The double core-shell fluorescent materials include inner
core, inner shell coating the inner core and outer shell coating the said
inner shell. The inner core is metal particle and the chemical
constitution of the inner shell is silicon dioxide. The outer shell is
fluorescent powder represented by the following chemical formula:
(R1-x, Eux)2O3, wherein R is Y, Gd or combination
thereof, 0.02≦x≦0.1. The double core-shell fluorescent
materials with uniform and stable luminous effect not only increase
luminous intensity, but also decrease usage amount of fluorescent powder
by using metal particle as inner core.

Claims:

1. A double core-shell fluorescent material, comprising: an inner core,
an inner shell coating the inner core, and an outer shell coating the
inner shell, the inner core is a metal particle, the chemical composition
of the inner shell is silicon dioxide, the outer shell is phosphor
represented by the following chemical formula: (R1-x,
Eux)2O3, wherein R is Y, Gd or a combination thereof,
0.02.ltoreq.x≦0.1.

2. The double core-shell fluorescent material according to claim 1,
wherein the metal particle is made of at least one of Ag, Au, Pt, and Pd.

3. The double core-shell fluorescent material according to claim 1,
wherein the particle size of the metal particle is in a range of 20 nm to
100 nm.

4. The double core-shell fluorescent material according to claim 1,
wherein the inner core is coated by the inner shell to form an
inner-coating structure, the inner-coating structure is a microsphere
structure.

5. The double core-shell fluorescent material according to claim 1,
wherein the outer shell covers the surface of the inner shell in a form
of layer, and the double core-shell fluorescent material is a spherical
or spherical-like particle.

6. A preparation method of a double core-shell fluorescent material,
comprising the following steps: obtaining a metal particle sol;
dissolving the metal particle sol into an alcohol solvent and weak
alkaline solution, adding tetraethyl orthosilicate to react and preparing
a suspension in which silicon dioxide coats a metal particle as an inner
shell; preparing a mixture solution containing at least one of yttrium
nitrate and gadolinium nitrate with europium nitrate, adding a
precipitant or gel, dissolving each nitrate salt and the precipitant or
gel utilizing solvent, and adding the suspension in which silicon dioxide
coats a metal particle as a inner shell to obtain a precursor of the
double core-shell fluorescent material; and calcining the precursor of
the double core-shell fluorescent material to form a phosphor outer shell
coating the silicon dioxide inner shell and represented by the following
chemical formula: (R1-x, Eux)2O3, wherein R is Y, Gd
or a combination thereof, 0.02.ltoreq.x≦0.1, and obtaining the
double core-shell fluorescent material.

7. The preparation method of a double core-shell fluorescent material
according to claim 6, after obtaining the metal particle sol, further
comprising surface treating the metal particle sol using surfactant with
a concentration of 0.001 g/ml to 0.01 g/ml with stirring for 3 hours to
12 hours.

8. The preparation method of a double core-shell fluorescent material
according to claim 6, further comprising repeating the step of obtaining
the precursor of the double core-shell fluorescent material, during each
repetition, using the previous obtained precursor to replace the
suspension in which silicon dioxide coats the metal particle as the inner
shell, to obtain the phosphor outer shell with desire thickness.

9. The preparation method of a double core-shell fluorescent material
according to claim 6, after preparing the mixture solution containing at
least one of yttrium nitrate and gadolinium nitrate with europium
nitrate, further comprising adding urea or oxalic acid as a precipitating
agent, mixing and dissolving the urea and oxalic acid, adding the
suspension in which silicon dioxide coats a metal particle as a inner
shell, adjusting the pH value utilizing ammonia, magnetic stirring for
0.5 hour to 1.5 hours, generating precipitate, filtering, washing,
drying, and obtaining the precursor having a outer shell composed by
europium, yttrium and/or gadolinium oxalate.

10. The preparation method of a double core-shell fluorescent material
according to claim 6, after preparing the mixture solution containing at
least one of yttrium nitrate and gadolinium nitrate with europium
nitrate, further comprising dissolving the mixture solution of nitrate
salt with a solvent, adding citric acid and polyethylene glycol, the
amount of the added citric acid is determined by a molar ratio of the
citric acid to the metal ions in the metal particle sol of 1.2:1 to 5:1,
and the amount of the added polyethylene glycol is determined that a
concentration of the polyethylene glycol of 0.08 g/ml to 0.2 g/ml, and
stirring and reacting in a water bath of 30.degree. C. to 60.degree. C.
for 4 hours to 8 hours to form a phosphor sol; adding the phosphor sol to
the suspension in which silicon dioxide coats a metal particle as a inner
shell, continuing to stir and reaction in a water bath of 60.degree. C.
to 90.degree. C. for 3 hours to 12 hours to obtain a gel.

11. The preparation method of a double core-shell fluorescent material
according to claim 6, after preparing the suspension in which silicon
dioxide coats a metal particle as a inner shell, further comprising
purifying, dispersing and dissolving the suspension, the purification
step comprises: centrifugal separating the suspension, washing with
distilled water or anhydrous ethanol to remove remaining weak alkaline
solution and residual tetraethyl orthosilicate; the dispersion and
dissolving step comprises: dispersing the suspension of the purification
step in distilled water using ultrasonic to obtain a purified suspension.

12. The preparation method of a double core-shell fluorescent material
according to claim 6, after preparing the suspension in which silicon
dioxide coats a metal particle as a inner shell, further comprising
adding surface modifier to the suspension with magnetic stirring, the
volume ratio of the surface modifier to the suspension is in a range of
5:1000 to 2:100, the magnetic stirring is for 2 hours to 4 hours to
obtain a surface modified suspension.

13. The preparation method of a double core-shell fluorescent material
according to claim 6, wherein the precursor of the double core-shell
fluorescent material is calcined at a temperature from 600.degree.
C.˜1400.degree. C. for 1 hour to 6 hours.

Description:

FIELD OF THE INVENTION

[0001] The present disclosure relates to luminescence materials
technologies, and more particularly relates to a double core-shell
fluorescent materials and preparation methods thereof.

BACKGROUND OF THE INVENTION

[0002] Rare earth luminescent material has become an important class of
optoelectronic materials. In recent years, with the development of
high-definition displays such as CRT, PDP, FED, etc., the requirement on
the morphology of the phosphor has become increasingly high. It is
usually considered the phosphor exhibiting a uniform particle size
distribution, distribution of monodisperse, non-reunion, and spherical
has a better application performance, because this type of phosphor has
advantages such as high packing density, low light scattering, high
resolution, and high brightness.

[0003] In considering of that, various methods have been developed to
optimize the morphology of the phosphor. For example, urea was used as
precipitant to prepare (Y, Tb)2O3 by coprecipitation so as to
obtain a spherical phosphor with uniform particle size distribution.
However, this spherical phosphor needs to use higher amounts of rare
earth raw materials, thus increasing the manufacturing costs, so it is
not suitable for industrial mass production and can not meet the wide
range of application needs of the lighting display.

[0004] Nowadays, the preparation of dual core-shell fluorescent materials
has become an important research focus in the field of luminescent
materials. As for commercialization, the luminescent properties of
obtained core-shell red fluorescent material is not ideal so far, and the
luminous intensity needs for further improvement. For example, a
SiO2@(Y, Eu)2O3 phosphor is designed and prepared
according to core-shell structure theory using (Y, Eu)2O3 to
coat SiO2. The phosphor can save the amount of the rare earth
element. However, the prepared SiO2@(Y, Eu)2O3 phosphor
has a low luminous intensity, resulting in that it cannot achieve
industrialization.

SUMMARY OF THE INVENTION

Technical Problems

[0005] In view of this, it is desired to provide a high luminous
efficiency, luminous uniform and stable double core-shell fluorescent
material.

[0006] And a simple, low cost preparation method of a double core-shell
fluorescent material is also provided.

Technical Solutions

[0007] A double core-shell fluorescent material includes an inner core, an
inner shell coating the inner core, and an outer shell coating the inner
shell, the inner core is a metal particle, the chemical composition of
the inner shell is silicon dioxide, the outer shell is phosphor
represented by the following chemical formula: (R1-x,
Eux)2O3, wherein R is Y, Gd or a combination thereof,
0.02≦x≦0.1.

[0008] A preparation method of a double core-shell fluorescent material
includes the following steps: [0009] obtaining a metal particle sol;
[0010] dissolving the metal particle sol into an alcohol solvent and weak
alkaline solution, adding tetraethyl orthosilicate to react and preparing
a suspension in which silicon dioxide coats a metal particle as an inner
shell; [0011] preparing a mixture solution containing at least one of
yttrium nitrate and gadolinium nitrate with europium nitrate, adding a
precipitant or gel, dissolving each nitrate salt and the precipitant or
gel utilizing solvent, and adding the suspension in which silicon dioxide
coats a metal particle as a inner shell to obtain a precursor of the
double core-shell fluorescent material; and [0012] calcining the
precursor of the double core-shell fluorescent material to form a
phosphor outer shell coating the silicon dioxide inner shell and
represented by the following chemical formula: (R1-x,
Eux)2O3, wherein R is Y, Gd or a combination thereof,
0.02≦x≦0.1, and obtaining the double core-shell fluorescent
material.

Beneficial Effects

[0013] The double core-shell fluorescent material, on the one hand, uses
dual-core-shell structure to greatly reduce the amount of the phosphor,
on the other hand, dual-core-shell structure is a monodisperse and can
well disperse the phosphor, such that the particle size distribution
uniformity and stability of the fluorescent material is increased, and
the fluorescent material exhibits a uniform and stable luminous
performance. In addition, since the metal particle is coated by the
phosphor, the fluorescence can be enhanced via a surface plasma resonance
produced by the metal particle, such that the double core-shell
fluorescent material has a greatly improved emitting performance compared
with the conventional fluorescent material, such as SiO2@(Y,
Eu)2O3. Referring to the preparation method, the double
core-shell fluorescent material is obtained by sol-gel method or
precipitation method with two steps of coating, which is simple, easy to
control, and has a low cost, thus having broad prospects for production
applications.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] These and other objects, advantages, purposes and features will
become apparent upon review of the following specification in conjunction
with the drawings.

[0015] FIG. 1 is a flowchart of an embodiment of a method for preparing a
double core-shell fluorescent material of the present disclosure;

[0016] FIG. 2 shows an emission spectrum of the fluorescent material
according to example 1 comparing with a conventional fluorescent
material;

[0017]FIG. 3 shows an emission spectrum of the fluorescent material
according to example 2 comparing with a conventional fluorescent
material;

[0018] FIG. 4 shows an emission spectrum of the fluorescent material
according to example 3 comparing with a conventional fluorescent
material;

[0019] FIG. 5 shows a photoluminescence spectrum of the fluorescent
material according to example 7 comparing with a conventional fluorescent
material;

[0020]FIG. 6 shows a cathode ray luminescence spectrum of the fluorescent
material according to example 7 comparing with a conventional fluorescent
material;

[0021]FIG. 7 shows a photoluminescence spectrum of the fluorescent
material according to example 8 comparing with a conventional fluorescent
material;

[0022] FIG. 8 shows a cathode ray luminescence spectrum of the fluorescent
material according to example 8 comparing with a conventional fluorescent
material;

[0023]FIG. 9 shows a photoluminescence spectrum of the fluorescent
material according to example 13 comparing with a conventional
fluorescent material;

[0024]FIG. 10 shows a cathode ray luminescence spectrum of the
fluorescent material according to example 13 comparing with a
conventional fluorescent material.

DETAILED DESCRIPTION

[0025] The disclosure is illustrated by way of example and not by way of
limitation in the figures of the accompanying drawings in which like
references indicate similar elements. It should be noted that references
to "an" or "one" embodiment in this disclosure are not necessarily to the
same embodiment, and such references mean at least one.

[0026] The present disclosure provides an embodiment of a double
core-shell fluorescent material, which includes an inner core, an inner
shell coating the inner core, and an outer shell coating the inner shell.
The inner core is a metal particle. The chemical composition of the inner
shell is silicon dioxide. The outer shell is phosphor represented by the
following chemical formula: (R1-x, Eux)2O3, wherein R
is Y, Gd or a combination thereof, 0.02≦x≦0.1.

[0027] The double core-shell can be represented by the following chemical
formula: M@SiO2@(R1-x, Eux)2O3, where @
represents coating. It should be noted that, the molar ratio of M,
SiO2, and (R1-x, Eux)2O3 is not shown in the
formula M@SiO2@(R1-x, Eux)2O3, instead, the
formula only indicates a double core-shell coating structure, i.e. the
three elements in the formula represent inner core, inner shell, and
outer shell in this order. Similarly, M@SiO2 and
M@SiO2@(Y1-x, Eux)2(C2O4)3, which will
be described later, have the same structure.

[0028] In detail, the metal particle is made of a metal having a good
stability to enhance the luminescence of the phosphor. Preferably, the
metal particle is made of at least one of Ag, Au, Pt, and Pd. The metal
particle is preferably nanoparticle having a particle size in a range of,
e.g., 20 nm to 100 nm.

[0029] The previously described double core-shell fluorescent material has
a double core-shell structure or double shell structure, in other words,
it has a double coating structure, namely inner-coating and
outer-coating. The inner-coating structure, which is formed by an inner
core coated by an inner shell, is a microsphere structure, or a
microsphere particle. The size of the microsphere particle may be in
magnitude of micron, e.g., 1 μm to 100 μm. The outer-coating
structure is formed by an inner shell coated by an outer shell , and is
also a microsphere structure, namely the shape of the outer shell is
spherical. The outer shell covers the surface of the inner shell in a
form of layer, that is the outer shell forms a phosphor layer represented
by the chemical formula: (R1-x, Eux)2O3. The whole
double core-shell fluorescent material is in a form of particle,
preferably spherical particle, or spherical-like particle.

[0030] In the previously described double core-shell fluorescent material,
the phosphor serves as a luminescence center. R is Y, Gd or a combination
of them. During irradiation, Y3+ and/or Gd3+ serves as active
ion, Eu3+ serves as a luminescence ion. In detail, when Y3+
and/or Gd3+ absorbs energy, it can transfer the energy to the
adjacent Eu3+ ion via a resonance energy transfer process, thus
irradiating Eu3+ to emit red light.

[0031] In the previously described double core-shell fluorescent material,
on the one hand, the amount of the phosphor is largely decreased by the
double core-shell structure, for example, the amount of the phosphor is
much less than that in the conventional single core-shell structure; on
the other hand, because the double core-shell structure is monodisperse,
which can well disperse the phosphor, the distribution uniformity and
stability of fluorescent material particle can be increased, thus
resulting in a better uniform and stable luminescence effect of the
fluorescent material. In addition, since the metal particle is coated by
the phosphor, the fluorescence can be enhanced via a surface plasma
resonance produced by the metal particle, such that the double core-shell
fluorescent material has a greatly improved emitting performance compared
with the conventional fluorescent material, such as SiO2@(Y,
Eu)2O3. Furthermore, the fluorescent material is spherical, and
the size and the morphology can be controlled. The spherical morphology
has a high bulk density, thus it is convenient for screen coating process
and can improve the display effect.

[0032] Referring to FIG. 1, a flowchart of an embodiment of a method for
preparing a double core-shell fluorescent material of the present
disclosure is shown. The method includes the following steps.

[0033] Step S01, a metal particle sol is obtained.

[0034] Step S02, a suspension containing M@SiO2 is prepared. The
metal particle sol is dissolved into an alcohol solvent and weak alkaline
solution, tetraethyl orthosilicate is added to react and a suspension in
which silicon dioxide coats a metal particle as an inner shell is
prepared.

[0035] Step S03, a precursor of the double core-shell fluorescent material
is obtained. A mixture solution containing at least one of yttrium
nitrate and gadolinium nitrate with europium nitrate is prepared, a
precipitant or gel is added, each nitrate salt and the precipitant or gel
are dissolved utilizing solvent, and the suspension in which silicon
dioxide coats a metal particle as a inner shell is added to obtain a
precursor of the double core-shell fluorescent material.

[0036] Step S04, the double core-shell fluorescent material is obtained.
The precursor of the double core-shell fluorescent material is calcined
to form a phosphor outer shell coating the silicon dioxide inner shell
and represented by the following chemical formula: (R1-x,
Eux)2O3, wherein R is Y, Gd or a combination thereof,
0.02≦x≦0.1.

[0037] In step S01, the metal particle can be provided directly, for
example, purchased commercially, or prepared. When the metal particle is
prepared, the preparation method includes the following steps.

[0038] 1) Suitable metal compound is weighted and dissolved into a solvent
to prepare and be diluted to a solution with certain concentration, e.g.,
2×10-4 mol/L˜1×10-3 mol/L. The metal compound
is preferably selected from the group consisting of silver nitrate,
chloroauric acid, chloric acid, palladium chloride, and the solvent is
preferably water and/or ethanol.

[0039] 2) One or more promoters are dissolved in the solution of step 1)
under magnetic stirring, and the concentration of the promoter in the
finally obtained metal nano-particle sol is in a range of
1.5×10-4 g/ml to 2.1×10-3 g/ml. The promoter is
preferably selected from the group consisting of polyethylene in N-methyl
pyrrolidone (PVP), sodium citrate, sixteen alkyl three methyl ammonium
bromide, sodium dodecyl sulfate, and sodium dodecyl sulfonate.

[0040] 3) A corresponding amount of reducing agent is dissolved in a
solvent to prepare a reducing solution having a concentration in a range
of 1×10-3 mol/L to 1×10-2 mol/L. The corresponding
amount of reducing agent is calculated approximately in accordance with
the stoichiometric amount to reduce the metal compounds. The reducing
agent is preferably hydrazine hydrate, ascorbic acid, or sodium
borohydride. The solvent is preferably water and/or ethanol.

[0041] 4) Under magnetic stirring, the reducing solution of step 3) is
added to the solution of step 2 in accordance with a molar ratio of the
reducing agent to the metal ion of 1.2:1 to 4.8:1. After a reaction of 10
min to 45 min, the metal nano-particle sol is obtained.

[0042] 5) In order to facilitate the coating of SiO2 on the metal
surface, the metal nano-particle sol is surface treated, which includes
the following steps. The metal nano-particle sol of step 4) is diluted
with deionized water to a concentration of 1×10-6 mol/L to
5×10-2 mol/L. A certain volume of the metal nano-particle sol
with the above concentration is measured, and surfactant is added with
stirring for 3 h to 12 h. The concentration of the surfactant is in a
range of 0.001 g/ml to 0.01 g/ml. In one embodiment, the volume of metal
nano-particle sol is measured for 0.5 ml to 10 ml, and the amount of the
surfactant is 0.01 g to 0.20 g, in which the ratio can be a reference
when mixing them in practice. The surfactant is preferably polyvinyl
pyrrolidone.

[0043] In step S02, the metal nano-particle sol after surface treatment is
further diluted to 10 ml to 20 ml. 10 ml to 50 ml of anhydrous ethanol
and 1 ml to 9 ml of ammonia are added with stirring. 0.5 ml to 6 ml of
tetraethyl orthosilicate (TEOS) is added under magnetic stirring. After
stirring for 1 hour to 6 hours at room temperature, a microsphere
suspension in which silicon dioxide coats a metal particle as an inner
shell can be obtained. Silicon dioxide coating a metal particle as an
inner shell is represented by M@SiO2. Anhydrous ethanol can be
replaced by other organic solvent, such as propyl alcohol and so on.
Ammonia can be replaced by other weak alkaline solution.

[0044] The microsphere suspension can be further purified, dispersed and
dissolved, or the microsphere suspension can be directly used. The
purification step includes: the suspension is centrifugal separated at a
rotational speed of 12000 rpm and washed with deionized water or ethanol
for three times to remove remaining weak alkaline solution and residual
TEOS, such that M@SiO2 microsphere can be obtained. The dispersion
and dissolving step includes: the M@SiO2 microsphere of the
purification step is dispersed in distilled water using ultrasonic to
obtain a purified M@SiO2 microsphere suspension.

[0045] In addition, the microsphere suspension is preferably surface
treated after or prior to the purification step or the dispersion and
dissolving step. In detail, a surface modifier is added to the
M@SiO2 microsphere suspension with magnetic stirring, where the
volume ratio of the surface modifier to the suspension is in a range of
5:1000 (v/v) to 2:100 (v/v). After the magnetic stirring for 2 h to 4 h,
a surface modified M@SiO2 microsphere suspension is obtained. The
surface modifier is preferably polyethyleneimine, 3-aminopropyl
trimethoxysilane or 3-aminopropyl triethoxysilane.

[0046] Step S03 may further includes the following sub-steps.

[0047] (1) A metal nitrate solution is selected. The metal source compound
can be metal oxide or nitrate. When metal oxides are used, yttrium oxide
and/or gadolinium oxide, europium oxide and other rare earth oxide are
added to a nitric acid solution (concentrated nitric acid), wetted by
deionized water, heated to dissolve to prepare a metal ion mixture
solution with a sum concentration of Y3+ and/or Gd3+, Eu3+
ions of 0.1 mol/L to 1 mol/L, in which a molar ratio of yttrium oxide
and/or gadolinium oxide to europium oxide is 0.98:0.02 to 0.9:0.1. When
metal nitrates are used, water serves as a solvent, a mixture solution
containing Eu(NO3)3 and Gd(NO3)3, or
Eu(NO3)3 and Y(NO3)3 is prepared according to a molar
ratio of Gd(NO3)3 to Eu(NO3)3, or Y(NO3)3
to Eu(NO3)3 is 0.98:0.02 to 0.9:0.1. The sum of concentration
of Y3+ and/or Gd3+ and Eu3+ in the mixture solution is in
a range of 0.5 mol/L to 2 mol/L.

[0048] (2) The precipitant or gel is added to the metal nitrate solution,
each nitrate salt and the precipitant or gel is dissolved utilizing
solvent, and the suspension in which silicon dioxide coats a metal
particle as the inner shell is added to obtain a precursor of the double
core-shell fluorescent material.

[0049] The step (2) may have two schemes. In the first scheme, the
precipitant, such as urea or oxalic acid, are used to precipitate. The
first scheme mainly includes the steps of preparing the precipitant,
mixing of the precipitant, the M@SiO2 microsphere suspension, and
the metal nitrate solution, the formation of the precipitate, etc. In
detail, the first scheme includes the following steps. The suspension in
which silicon dioxide coats a metal particle as the inner shell is added
to the metal nitrate solution, urea or oxalic acid is added and dissolved
with deionized water, the pH value is adjusted utilizing ammonia,
magnetic stirred, precipitate is generated, filtered, washed, dried, and
a white powder represented by the chemical formula
M@SiO2@(Y1-x, Eux)2(C2O4)3 is
obtained, which is the precursor of double core-shell fluorescent
material.

[0050] In a specific embodiment, the first scheme includes the following
steps:

[0052] ii. Urea or oxalic acid is weighted according to an overdose of 1.2
to 5.0 times and dissolved in the deionized water to prepare a urea or
oxalic acid solution with a concentration of 0.5 mol/L to 2 mol/L.

[0053] iii. The prepared urea or oxalic acid solution is added in drops to
the mixture solution of step i. The adding time is controlled to 30 min
to 80 min. After adding in drops, the solution is magnetic stirred for 2
h to 5 h, and the pH value of the reaction system is adjusted to 7 to 10,
and continue magnetic stirring for 0.5 h to 1.5 h.

[0054] vi. The product of the step iii is washed and filtered by deionized
water and ethanol for three times, and the filtered product is dried in a
80° C. to 100° C. oven for 2 h to 4 h, so as to obtain a
white powder of M@SiO2@(Y1-x,
Eux)2(C2O4)3.

[0055] Furthermore, in order to increase the thickness of the outer shell,
step i to step vi can be repeated for a number of times, in which the
M@SiO2 microsphere is replaced by the product of previous step vi.

[0056] In another embodiment, the first scheme includes the following
steps:

[0057] i) Preparation of the precipitant solution: oxalic acid or urea is
dissolved in deionized water, heated to dissolve into 0.1 mol/L to 1.5
mol/L oxalic acid or urea solution, and then ammonia is added to adjust
the solution pH value to 7 to 10.

[0058] ii) Preparation of the precursor of double core-shell fluorescent
material (M@SiO2@(Y1-x, Eux)2(C2O4)3).
The nitrate salt mixed solution is added into the M@SiO2 ethanol
solution with stirring. The oxalic acid and ammonia mixture solution with
a pH value of 9 is added in drops into the mixture of metal ions and
M@SiO2 mixture, in which the amount of the oxalic acid is 1.5 to 5
times of the molar amount of the rare earth ion. The rate of drops is 1
mL/min to 4 mL/min. The temperature of the solution is 20° C. to
75° C. After the adding in drops, the solution is stirred until
the reaction is over and a pH value of the solution is between 7 and 9.
The solution is aged for 1˜24 h, filtered and washed with deionized
water at least once, then with ethanol wash at least once, to obtain the
white precipitate. The white precipitate is dried in a 50°
C.˜120° C. oven for 3 h to 15 h to remove the water and
obtain white powder of M@SiO2@(Y1-x,
Eux)2(C2O4)3. Similarly, in order to increase
the thickness of the outer shell, step ii can be repeated for a number of
times, in which the M@SiO2 microsphere is replaced by the product of
previous step ii.

[0059] The second scheme mainly includes the steps of preparing rare earth
metal particle sol and gel, and so on. In detail, the second scheme
includes the following steps. The nitrate of yttrium and/or gadolinium,
europium is dissolved using solvents such as ethanol or water, citric
acid is added, and the amount of the citric acid is determined according
to the molar ratio of 1.2:1 to 5:1 that the citric acid and the metal ion
in the metal particle gel. The solution is stirred, polyethylene glycol
is added and the concentration of the polyethylene glycol in the solution
is 0.08 g/ml to 0.2 g/ml. The solution is then stirred in a 30° C.
to 60° C. water bath for 4 h to 8 h to prepare a phosphor sol. The
phosphor sol is added into the M@SiO2 suspension and stirred in a
60° C. to 90° C. water bath for 3 h to 12 h to obtain a
gel, which is the precursor of the double core-shell fluorescent
material. Citric acid and polyethylene glycol are used as the gel, and
the adding order is not limited to the described embodiment.

[0060] In a specific embodiment, the second scheme includes the following
steps:

[0061] a) According to a ratio of ethanol to water of 3:1 to 9:1, ethanol
is added to the nitrate mixture of 1), a corresponding amount of citric
acid is added to the mixed solution with stirring. The amount of the
citric acid is determined according to a molar ratio of the citric acid
to the metal ion (Y3+ and/or Gd3+, Eu3+) in the metal
particle gel of 1.2:1 to 5:1.

[0062] b) PEG (polyethylene glycol) is added into the mixture solution of
step a) and a concentration of the PEG in the system is in a range of
0.08 g/mL to 0.2 g/mL. The solution is then stirred and reacted in a
30° C. to 60° C. water bath for 4 h to 8 h to prepare a
sol.

[0063] c) The M@SiO2 suspension of step S02 is added into the sol of
step b), the solution is then stirred in a 60° C. to 90° C.
water bath for 3 h to 12 h to obtain a gel.

[0064] d) The gel of step c) is dried in an 80° C. to 100°
C. oven for 2 h to 4 h.

[0065] Similarly, in order to increase the thickness of the outer shell,
step c) can be repeated for a number of times, in which the M@SiO2
microsphere in step c) is replaced by the product of previous step d)
(i.e. the previous obtained precursor).

[0066] In step S04, the precursor of the double core-shell fluorescent
material of step S03 is calcined at a temperature of 600° C. to
1400° C. for 1 h to 6 h to obtain the double core-shell
fluorescent material of M@SiO2@(Y1-x,
Eux)2(C2O4)3. The calcination temperature is
preferably 800° C. to 1200° C., the calcination time is
preferably 2 h to 3 h. The above scheme is known as the Pechini sol-gel
method.

[0067] The specific compounds are described to illustrate the double
core-shell fluorescent material of different composition and preparation
methods, as well as its performance.

Example 1

[0068] Under room temperature, 0.5 ml of Au particle sol having average
particle size of 20 nm, the concentration of 5×10-2 mol/L was
measured and placed in a beaker. 0.01 g of PVP was added with stirring.
After 3 h of stirring, 20 ml of ethanol, 2 ml of deionized water, 2 ml of
ammonia, and 1 ml of TEOS were added in that order. After stirred for 5
h, the solution is centrifuged to obtain Au@SiO2 microsphere
particles, which is then washed with ethanol for three times, poured into
a conical flask.

[0069] 2.1226 g of yttria oxide and 0.21111 g of europium oxide were
weighted and wetted by deionized water, dissolved by 5 ml of nitric acid
to produce a metal nitrate mixed solution, the sum metal ion
concentration of which is 0.1 mol/L. The metal nitrate mixed solution was
poured into Au@SiO2 ethanol solution and stirred to prepare a
mixture solution A.

[0070] 3.7821 g of oxalic acid was weighted and dissolved in deionized
water, ammonia was add to adjust the pH value to 9 and prepare a 0.1
mol/L of a mixed solution of oxalic acid and ammonia. The mixed solution
of oxalic acid and ammonia was then added in drops to the mixture
solution A by a rate of 2 ml/min. After the dropping, ammonia was added
to adjust the pH value to 7, the solution was aged for 12 h and filtered,
the precipitation was washed with deionized water and ethanol for three
times and then moved into a 60° C. oven to dry for 15 h to obtain
a white powder. The white powder is heat treated at 1100° C. for 2
h to obtain a double core-shell phosphor of Au@SiO2@(Y0.94,
Eu0.06)2O3.

Example 2

[0071] Under room temperature, 1 ml of Pt particle sol having average
particle size of 100 nm, the concentration of 1×10-6 mol/L was
measured and placed in a beaker. 0.20 g of PVP was added with stirring.
After 12 h of stirring, 10 ml of ethanol, 10 ml of deionized water, 1 ml
of ammonia, and 1 ml of TEOS were added in that order. After stirred for
3 h, the solution is centrifuged to obtain Pt@SiO2 microsphere
particles, which is then washed with ethanol for five times, poured into
a conical flask.

[0072] 2.2558 g of yttria oxide and 0.0035 g of europium oxide were
weighted and wetted by deionized water, dissolved by 5 ml of nitric acid
to produce a metal nitrate mixed solution, the sum metal ion
concentration of which is 0.5 mol/L. The metal nitrate mixed solution was
poured into Pt@SiO2 ethanol solution and stirred to prepare a
mixture solution A.

[0073] 4.9167 g of oxalic acid was weighted and dissolved in deionized
water, ammonia was add to adjust the pH value to 9 and prepare a 1.5
mol/L of a mixed solution of oxalic acid and ammonia. The mixed solution
of oxalic acid and ammonia was then added in drops to the mixture
solution A by a rate of 2 ml/min. After the dropping, ammonia was added
to adjust the pH value to 9, the solution was aged for 1 h and filtered,
the precipitation was washed with deionized water and ethanol for three
times and then moved into a 50° C. oven to dry for 15 h to obtain
a white powder. The white powder is heat treated at 1400° C. for 1
h to obtain a double core-shell phosphor of Pt@SiO2@(Y0.999,
Eu0.001)2O3.

Example 3

[0074] Under room temperature, 2 ml of Ag particle sol having average
particle size of 60 nm, the concentration of 3×10-6 mol/L was
measured and placed in a beaker. 0.15 g of PVP was added with stirring.
After 6 h of stirring, 14 ml of ethanol, 8 ml of deionized water, 3 ml of
ammonia, and 2 ml of TEOS were added in that order. After stirred for 1
h, the solution is centrifuged to obtain Ag@SiO2 microsphere
particles, which is then washed with ethanol for four times, poured into
a conical flask.

[0075] 2.1000 g of yttria oxide and 0.2463 g of europium oxide were
weighted and wetted by deionized water, dissolved by 5 ml of nitric acid
to produce a metal nitrate mixed solution, the sum metal ion
concentration of which is 1 mol/L. The metal nitrate mixed solution was
poured into Ag@SiO2 ethanol solution and stirred to prepare a
mixture solution A.

[0076] 6.3035 g of oxalic acid was weighted and dissolved in deionized
water, ammonia was add to adjust the pH value to 9 and prepare a 0.5
mol/L of a mixed solution of oxalic acid and ammonia. The mixed solution
of oxalic acid and ammonia was then added in drops to the mixture
solution A by a rate of 2 ml/min. After the dropping, ammonia was added
to adjust the pH value to 10, the solution was aged for 24 h and
filtered, the precipitation was washed with deionized water and ethanol
for three times and then moved into a 120° C. oven to dry for 3 h
to obtain a white powder. The white powder is heat treated at 800°
C. for 4 h to obtain a double core-shell phosphor of
Ag@SiO2@(Y0.93, Eu0.07)2O3.

Example 4

[0077] Under room temperature, 1 ml of Pd particle sol having average
particle size of 80 nm, the concentration of 5×10-3 mol/L was
measured and placed in a beaker. 0.12 g of PVP was added with stirring.
After 10 h of stirring, 16 ml of ethanol, 5 ml of deionized water, 1.5 ml
of ammonia, and 0.5 ml of TEOS were added in that order. After stirred
for 6 h, the solution is centrifuged to obtain Pd@SiO2 microsphere
particles, which is then washed with ethanol for three times, poured into
a conical flask.

[0078] 2.1904 g of yttria oxide and 0.1056 g of europium oxide were
weighted and wetted by deionized water, dissolved by 5 ml of nitric acid
to produce a metal nitrate mixed solution, the sum metal ion
concentration of which is 0.2 mol/L. The metal nitrate mixed solution was
poured into Pd@SiO2 ethanol solution and stirred to prepare a
mixture solution A.

[0079] 4.9167 g of oxalic acid was weighted and dissolved in deionized
water, ammonia was add to adjust the pH value to 9 and prepare a 0.8
mol/L of a mixed solution of oxalic acid and ammonia. The mixed solution
of oxalic acid and ammonia was then added in drops to the mixture
solution A by a rate of 2 ml/min. After the dropping, ammonia was added
to adjust the pH value to 8, the solution was aged for 12 h and filtered,
the precipitation was washed with deionized water and ethanol for three
times and then moved into a 90° C. oven to dry for 8 h to obtain a
white powder. The white powder is heat treated at 1000° C. for 3 h
to obtain a double core-shell phosphor of Pd@SiO2@(Y0.97,
Eu0.03)2O3.

Example 5

[0080] Under room temperature, 1 ml of Ag particle sol having average
particle size of 80 nm, the concentration of 3×10-5 mol/L was
measured and placed in a beaker. 0.10 g of PVP was added with stirring.
After 6 h of stirring, 15 ml of ethanol, 85 ml of deionized water, 1 ml
of ammonia, and 2 ml of TEOS were added in that order. After stirred for
4 h, the solution is centrifuged to obtain Ag@SiO2 microsphere
particles, which is then washed with ethanol for three times, poured into
a conical flask.

[0081] 2.1000 g of yttria oxide and 0.2463 g of europium oxide were
weighted and wetted by deionized water, dissolved by 5 ml of nitric acid
to produce a metal nitrate mixed solution, the sum metal ion
concentration of which is 1 mol/L. The metal nitrate mixed solution was
poured into Ag@SiO2 ethanol solution and stirred to prepare a
mixture solution A.

[0082] 5.6732 g of oxalic acid was weighted and dissolved in deionized
water, ammonia was add to adjust the pH value to 9 and prepare a 1 mol/L
of a mixed solution of oxalic acid and ammonia. The mixed solution of
oxalic acid and ammonia was then added in drops to the mixture solution A
by a rate of 3 ml/min. After the dropping, ammonia was added to adjust
the pH value to 8, the solution was aged for 24 h and filtered, the
precipitation was washed with deionized water and ethanol for three times
and then moved into a 100° C. oven to dry for 5 h to obtain a
white powder. The white powder is heat treated at 900° C. for 4 h
to obtain a double core-shell phosphor of Ag@SiO2@(Y0.93,
Eu0.07)2O3.

Example 6

[0083] Preparation of the Pt nano-particle sol: 5.18 mg of chloroplatinic
acid (H2PtCl6.6H2O) was dissolved into 17 ml of deionized
water. When the chloroplatinic acid was completely dissolved, 8.0 mg of
sodium citrate and 12.0 mg of sodium dodecyl sulfate were weighted and
dissolved in the chloroplatinic acid solution with magnetic stirring.
0.38 mg of sodium borohydride was dissolved into 10 ml of deionized water
to prepare a 10 ml of sodium borohydride aqueous solution with the
concentration of 1×10-3 mol/L. 10 ml of hydrazine hydrate
solution with the concentration of 1×10-2 mol/L was prepared
at the same time. Under magnetic stirring, 0.4 ml of sodium borohydride
aqueous solution was added in drops into the chloroplatinic acid
solution, stirred for 5 min, 2.6 ml of hydrazine hydrate solution with
the concentration of 1×10-2 mol/L was then added in drops into
the chloroplatinic acid aqueous solution, continuing to react for 40 min
to prepare 20 ml of Pt nano-particle sol. 6.0 mg of PVP was added into 6
ml of Pt nano-particle sol with magnetic stirring for 12 h to obtain a
surface treated Pt nano-particle.

[0084] Preparation of Pt@SiO2 microsphere and surface modification: 6 ml
of surface treated Pt nano-particle is diluted with deionized water to 10
ml. Followed by adding 15 ml of anhydrous ethanol and 1 ml of ammonia
with magnetic stirring. 0.5 ml of TEOS is added in drops under stirring.
After the dropping, the mixture was stirred for 2 h to obtain a Pt
@SiO2 microsphere suspension. The obtained Pt@SiO2 microsphere
suspension was centrifuged by a speed of 12000 rpm, washed three times
with deionized water, to remove the remaining ammonia and residual TEOS,
to obtain a purified Pt@SiO2 microsphere. The obtained Pt@SiO2
microsphere was dispersed into deionized water via ultrasonic to prepare
10 ml of Pt@SiO2 suspension. In the environment of magnetic
stirring, 0.1 ml of surface modifier, polyethylene imine, was added into
10 ml suspension, and then stirred for 2 h to obtain surface modified of
Pt@SiO2 microsphere suspension, which is denoted by A1.

[0085] Preparation of Pt@SiO2@(Gd0.98,
Eu0.02)2O3. 1.774 g of Gd2O3 and 0.0352 g of
Eu2O3 were weighted according to a molar ratio of
Gd(NO3)3 to Eu(NO3)3 of 0.98:0.02. Gd2O3
and Eu2O3 were dissolved with concentrated nitric acid to
prepare 10 ml of mixture solution containing Gd(NO3)3 and
Eu(NO3)3, in which the sum concentration of the Gd3+ and
Eu3+ is 0.5 mol/L. The mixture solution containing
Gd(NO3)3 and Eu(NO3)3 was added to the obtained
suspension A1, magnetic stirred for 1 h to prepare a mixture solution
denoted by B1. 1.5306 g of urea which overdosed for five times was
weighted and dissolved in 25.5 ml of deionized water to prepare a urea
solution with a concentration of 1 mol/L. The urea solution was added in
drops into the mixture solution B1 for 30 min. After the dropping,
continue to stir for 2 h, the pH value of the system was adjusted to 7,
continue to stir for 1.5 h to prepare a suspension denoted by C1. The
suspension C1 was washed and filtered with deionized water and ethanol
for three times, and filtration product was dried in an 80° C.
oven for 4 h. The coating step was repeated for three times. The finally
obtained dried product was calcined at a high temperature of 800°
C. for 6 h to obtain a double core-shell fluorescent material of
Pt@SiO2@(Gd0.98, Eu0.02)2O3.

Example 7

[0086] Preparation of the Au nano-particle sol: 4.12 mg of chloroauric
acid (H2AuCl6.6H2O) was dissolved into 8.4 ml of deionized
water. When the chloroauric acid was completely dissolved, 14 mg of
sodium citrate and 6 mg of cetyl trimethyl ammonium bromide were weighted
and dissolved in the chloroauric acid solution with magnetic stiffing.
1.9 mg of sodium borohydride and 17.6 mg of ascorbic acid were dissolved
into 10 ml of deionized water respectively to prepare 10 ml of sodium
borohydride aqueous solution with the concentration of 5×10-3
mol/L and 10 ml of ascorbic acid aqueous solution with the concentration
of 1×10-2 mol/L. Under magnetic stirring, 0.04 ml of sodium
borohydride aqueous solution was added in drops into the chloroauric acid
solution, stirred for 5 min, 1.56 ml of ascorbic acid aqueous solution
with the concentration of 1×10-2 mol/L was then added in drops
into the chloroauric acid aqueous solution, continuing to react for 30
min to prepare 10 ml of Au nano-particle sol with a concentration of
1×10-3 mol/L. 10 mg of PVP was added into 6 ml of Au
nano-particle sol with magnetic stirring for 8 h to obtain a surface
treated Au nano-particle.

[0087] Preparation of Au@SiO2 microsphere and surface modification: 6 ml
of surface treated Au nano-particle is diluted with deionized water to 10
ml. Followed by adding 25 ml of anhydrous ethanol and 4 ml of ammonia
with magnetic stirring. 1 ml of TEOS is added in drops under stirring.
After the dropping, the mixture was stirred for 3 h to obtain an
Au@SiO2 microsphere suspension. The obtained Au@SiO2
microsphere suspension was centrifuged by a speed of 12000 rpm, washed
three times with deionized water, to remove the remaining ammonia and
residual TEOS, to obtain a purified Au@SiO2 microsphere. The
obtained Au@SiO2 microsphere was dispersed into deionized water via
ultrasonic to prepare 10 ml of Au@SiO2 suspension. In the
environment of magnetic stirring, 0.2 ml of surface modifier,
3-aminopropyl trimethoxysilane, was added into 10 ml suspension, and then
stirred for 2 h to obtain surface modified of Au@SiO2 microsphere
suspension, which is denoted by A2.

[0088] Preparation of Au@SiO2@(Gd0.95,
Eu0.05)2O3. 3.620 g of Gd2O3 and 0.1853 g of
Eu2O3 were weighted according to a molar ratio of
Gd(NO3)3 to Eu(NO3)3 of 0.95:0.05. Gd2O3
and Eu2O3 were dissolved with concentrated nitric acid to
prepare 20 ml of mixture solution containing Gd(NO3)3 and
Eu(NO3)3, in which the sum concentration of the Gd3+ and
Eu3+ is 0.53 mol/L. The mixture solution containing
Gd(NO3)3 and Eu(NO3)3 was added to the obtained
suspension A2, magnetic stirred for 2 h to prepare a mixture solution
denoted by B2. 2.3874 g of oxalic acid which overdosed for 1.2 times was
weighted and dissolved in 18.9 ml of deionized water to prepare an oxalic
acid solution with a concentration of 1 mol/L. The oxalic acid solution
was added in drops into the mixture solution B2 for 40 min. After the
dropping, continue to stir for 3 h, the pH value of the system was
adjusted to 9, continue to stir for 1 h to prepare a suspension denoted
by C2. The suspension C2 was washed and filtered with deionized water and
ethanol for three times, and filtration product was dried in a
100° C. oven for 2 h. The finally obtained dried product was
calcined at a high temperature of 1000° C. for 4 h to obtain a
double core-shell fluorescent material of Au@SiO2@(Gd0.95,
Eu0.05)2O3.

Example 8

[0089] Preparation of the Ag nano-particle sol: 3.40 mg of silver nitrate
(AgNO3) was dissolved into 18.4 ml of deionized water. When the
silver nitrate was completely dissolved, 42 mg of sodium citrate was
weighted and dissolved in the silver nitrate solution with magnetic
stirring. 5.7 mg of sodium borohydride was dissolved into 10 mL deionized
water to obtain 10 ml sodium borohydride aqueous solution with a
concentration of 1.5×10-2 mol/L. Under magnetic stirring, 1.6
ml of sodium borohydride aqueous solution with a concentration of
1.5×10-2 mol/L was added to the silver nitrate, continuing to
react for 10 min to prepare 20 ml of Ag nano-particle sol with a
concentration of 1×10-3 mol/L. 40 mg of PVP was added into 8
ml of Ag nano-particle sol with magnetic stirring for 6 h to obtain a
surface treated Ag nano-particle.

[0090] Preparation of Ag@SiO2 microsphere and surface modification: 8 ml
of surface treated Ag nano-particle is diluted with deionized water to 10
ml. Followed by adding 30 ml of anhydrous ethanol and 6 ml of ammonia
with magnetic stirring. 2 ml of TEOS is added in drops under stirring.
After the dropping, the mixture was stirred for 3 h to obtain an
Ag@SiO2 microsphere suspension. The obtained Au @SiO2
microsphere suspension was centrifuged by a speed of 12000 rpm, washed
three times with deionized water, to remove the remaining ammonia and
residual TEOS, to obtain a purified Ag@SiO2 microsphere. The
obtained Ag@SiO2 microsphere was dispersed into deionized water via
ultrasonic to prepare 20 ml of Ag@SiO2 suspension. In the
environment of magnetic stirring, 0.2 ml of surface modifier,
polyethylenimine, was added into 20 ml of Ag@SiO2 suspension, and
then stirred for 3 h to obtain surface modified of Ag@SiO2
microsphere suspension, which is denoted by A3.

[0091] Preparation of Ag@SiO2@(Gd0.94,
Eu0.06)2O3. 4.344 g of Gd2O3 and 0.2996 g of
Eu2O3 were weighted according to a molar ratio of
Gd(NO3)3 to Eu(NO3)3 of 0.94:0.06. Gd2O3
and Eu2O3 were dissolved with concentrated nitric acid to
prepare 20 ml of mixture solution containing Gd(NO3)3 and
Eu(NO3)3, in which the sum concentration of the Gd3+ and
Eu3+ is 0.638 mol/L. The mixture solution containing
Gd(NO3)3 and Eu(NO3)3 was added to the obtained
suspension A3, magnetic stirred for 2 h to prepare a mixture solution
denoted by B3. 3.150 g of oxalic acid which overdosed for 1.3 times was
weighted and dissolved in 50 ml of deionized water to prepare an oxalic
acid solution with a concentration of 0.5 mol/L. The oxalic acid solution
was added in drops into the mixture solution B3 for 60 min. After the
dropping, continue to stir for 3 h, the pH value of the system was
adjusted to 9, continue to stir for 1 h to prepare a suspension denoted
by C3. The suspension C3 was washed and filtered with deionized water and
ethanol for three times, and filtration product was dried in a 90°
C. oven for 3 h. The finally obtained dried product was calcined at a
high temperature of 1000° C. for 4 h to obtain a double core-shell
fluorescent material of Ag@SiO2@(Gd0.94,
Eu0.06)2O3.

Example 9

[0092] Preparation of the Pd nano-particle sol: 0.43 mg of palladium
chloride (PdCl2.2H2O) was dissolved into 8.5 ml of deionized
water. When the palladium chloride was completely dissolved, 11.0 mg of
sodium citrate and 4.0 mg of sodium dodecyl sulfate were weighted and
dissolved in the palladium chloride solution with magnetic stirring. 3.8
mg of sodium borohydride was dissolved into 10 mL deionized water to
obtain 10 ml sodium borohydride aqueous solution with a concentration of
1×10-2 mol/L. Under magnetic stirring, 0.48 ml of sodium
borohydride aqueous solution with a concentration of 1×10-2
mol/L was added to the palladium chloride aqueous solution, continuing to
react for 20 min to prepare 10 ml of Pd nano-particle sol with a
concentration of 1×10-4 mol/L. 50 mg of PVP was added into 10
ml of Pd nano-particle sol with magnetic stirring for 4 h to obtain a
surface treated Pd nano-particle.

[0093] Preparation of Pd@SiO2 microsphere and surface modification:
10 ml of surface treated Pd nano-particle was diluted with deionized
water to 15 ml. Followed by adding 40 ml of anhydrous ethanol and 7 ml of
ammonia with magnetic stirring. 4 ml of TEOS is added in drops under
stirring. After the dropping, the mixture was stirred for 4 h to obtain a
Pd@SiO2 microsphere suspension. The obtained Pd@SiO2
microsphere suspension was centrifuged by a speed of 12000 rpm, washed
three times with deionized water, to remove the remaining ammonia and
residual TEOS, to obtain a purified Pd@SiO2 microsphere. The
obtained Pd@SiO2 microsphere was dispersed into deionized water via
ultrasonic to prepare 30 ml of Pd@SiO2 suspension. In the
environment of magnetic stirring, 0.4 ml of surface modifier,
3-aminopropyl triethoxysilane, was added into 30 ml of Pd@SiO2
suspension, and then stirred for 2 h to obtain surface modified of
Pd@SiO2 microsphere suspension, which is denoted by A4.

[0094] Preparation of Pd@SiO2@(Gd0.92,
Eu0.08)2O3. 7.240 g of Gd2O3 and 0.6121 g of
Eu2O3 were weighted according to a molar ratio of
Gd(NO3)3 to Eu(NO3)3 of 0.92:0.08. Gd2O3
and Eu2O3 were dissolved with concentrated nitric acid to
prepare 21.7 ml of mixture solution containing Gd(NO3)3 and
Eu(NO3)3, in which the sum concentration of the Gd3+ and
Eu3+ is 1 mol/L. The mixture solution containing Gd(NO3)3
and Eu(NO3)3 was added to the obtained suspension A4, magnetic
stirred for 3 h to prepare a mixture solution denoted by B4. 5.752 g of
oxalic acid which overdosed for 1.4 times was weighted and dissolved in
25 ml of deionized water to prepare an oxalic acid solution with a
concentration of 1.83 mol/L. The oxalic acid solution was added in drops
into the mixture solution B4 for 70 min. After the dropping, continue to
stir for 4 h, the pH value of the system was adjusted to 11, continue to
stir for 0.5 h to prepare a suspension denoted by C4. The suspension C4
was washed and filtered with deionized water and ethanol for three times,
and filtration product was dried in a 100° C. oven for 2 h. The
finally obtained dried product was calcined at a high temperature of
1100° C. for 3 h to obtain a double core-shell fluorescent
material of Pd@SiO2g(Gd0.92, Eu0.08)2O3.

Example 10

[0095] Preparation of the Ag nano-particle sol: 3.40 mg of silver nitrate
(AgNO3) was dissolved into 18.4 ml of ethanol. When the silver
nitrate was completely dissolved, 35.5 mg of PVP was weighted and
dissolved in the silver nitrate ethanol solution with magnetic stirring.
5.7 mg of sodium borohydride was dissolved into 10 ml ethanol to obtain
10 ml sodium borohydride ethanol solution with a concentration of
1.5×10-2 mol/L. Under magnetic stirring, 1.6 ml of sodium
borohydride ethanol solution with a concentration of 1.5×10-2
mol/L was added to the silver nitrate ethanol solution, continuing to
react for 15 min to prepare 20 ml of Ag nano-particle sol with a
concentration of 1×10-3 mol/L. 100 mg of PVP was added into 10
ml of Ag nano-particle sol with magnetic stirring for 3 h to obtain a
surface treated Ag nano-particle.

[0096] Preparation of Ag@SiO2 microsphere and surface modification:
10 ml of surface treated Ag nano-particle is diluted with deionized water
to 20 ml. Followed by adding 50 ml of anhydrous ethanol and 9 ml of
ammonia with magnetic stirring. 6 ml of TEOS is added in drops under
stirring. After the dropping, the mixture was stirred for 6 h to obtain
an Ag@SiO2 microsphere suspension. The obtained Au @SiO2
microsphere suspension was centrifuged by a speed of 12000 rpm, washed
three times with deionized water, to remove the remaining ammonia and
residual TEOS, to obtain a purified Ag@SiO2 microsphere. The
obtained Ag@SiO2 microsphere was dispersed into deionized water via
ultrasonic to prepare 40 ml of Ag@SiO2 suspension. In the
environment of magnetic stirring, 0.2 ml of surface modifier,
3-aminopropyl triethoxysilane, was added into 40 ml of Ag@SiO2
suspension, and then stirred for 4 h to obtain surface modified of
Ag@SiO2 microsphere suspension, which is denoted by A5.

[0097] Preparation of Ag@SiO2@(Gd0.90, Eu0.1)2O3.
9.774 g of Gd2O3 and 1.056 g of Eu2O3 were weighted
according to a molar ratio of Gd(NO3)3 to Eu(NO3)3 of
0.90:0.10. Gd2O3 and Eu2O3 were dissolved with
concentrated nitric acid to prepare 15 ml of mixture solution containing
Gd(NO3)3 and Eu(NO3)3, in which the sum concentration
of the Gd3+ and Eu3+ is 2 mol/L. The mixture solution
containing Gd(NO3)3 and Eu(NO3)3 was added to the
obtained suspension A5, magnetic stirred for 4 h to prepare a mixture
solution denoted by B5. 8.505 g of oxalic acid which overdosed for 1.5
times was weighted and dissolved in 34 ml of deionized water to prepare
an oxalic acid solution with a concentration of 2 mol/L. The oxalic acid
solution was added in drops into the mixture solution B5 for 80 min.
After the dropping, continue to stir for 5 h, the pH value of the system
was adjusted to 12, continue to stir for 0.5 h to prepare a suspension
denoted by C5. The suspension C5 was washed and filtered with deionized
water and ethanol for three times, and filtration product was dried in a
100° C. oven for 3 h. The finally obtained dried product was
calcined at a high temperature of 1200° C. for 2 h to obtain a
double core-shell fluorescent material of Ag@SiO2@(Gd0.90,
EU0.10)2O3.

Example 11

[0098] Preparation of the Pt nano-particle sol: 5.18 mg of chloroplatinic
acid (H2PtCl6.6H2O) was dissolved into 17 ml of deionized
water. When the chloroplatinic acid was completely dissolved, 8.0 mg of
sodium citrate and 12.0 mg of sodium dodecyl sulfate were weighted and
dissolved in the chloroplatinic acid solution with magnetic stirring.
0.38 mg of sodium borohydride was dissolved into 10 ml of deionized water
to prepare a 10 ml of sodium borohydride aqueous solution with the
concentration of 1×10-3 mol/L. 10 ml of hydrazine hydrate
solution with the concentration of 1×10-2 mol/L was prepared
at the same time. Under magnetic stirring, 0.4 ml of sodium borohydride
aqueous solution was added in drops into the chloroplatinic acid
solution, stirred for 5 min, 2.6 ml of hydrazine hydrate solution with
the concentration of 1×10-2 mol/L was then added in drops into
the chloroplatinic acid aqueous solution, continuing to react for 40 min
to prepare 20 ml of Pt nano-particle sol with a concentration of
5×10-4 mol/L. 6.0 mg of PVP was added into Pt nano-particle
sol with magnetic stirring for 12 h to obtain a surface treated Pt
nano-particle.

[0099] Preparation of Pt@SiO2 microsphere and surface modification: 6 ml
of surface treated Pt nano-particle is diluted with deionized water to 10
ml. Followed by adding 15 ml of anhydrous ethanol and 1 ml of ammonia
with magnetic stirring. 0.5 ml of TEOS is added in drops under stirring.
After the dropping, the mixture was stirred for 2 h to obtain a
Pt@SiO2 microsphere suspension. The obtained Pt@SiO2
microsphere suspension was centrifuged by a speed of 12000 rpm, washed
three times with deionized water, to remove the remaining ammonia and
residual TEOS, to obtain a purified Pt@SiO2 microsphere. The
obtained Pt@SiO2 microsphere was dispersed into deionized water via
ultrasonic to prepare 10 ml of Pt@SiO2 suspension.

[0100] Preparation of Pt@SiO2@(Gd0.98,
Eu0.02)2O3. 1.774 g of Gd2O3 and 0.0352 g of
Eu2O3 were weighted according to a molar ratio of
Gd(NO3)3 to Eu(NO3)3 of 0.98:0.02. Gd2O3
and Eu2O3 were dissolved with concentrated nitric acid to
prepare 10 ml of mixture solution containing Gd(NO3)3 and
Eu(NO3)3, in which the sum concentration of the Gd3+ and
Eu3+ is 0.5 mol/L. 90 ml of ethanol and 4.80 g citric acid were add
into nitrate mixture solution, after stirring, 10 g of PEG was added, the
solution was stirred in a 30° C. of water bath for 8 h in form a
sol. The prepared Pt@SiO2 suspension was added into the sol, the
solution was stirred in a 60° C. of water bath for 12 h to form a
gel. The gel was dried in an 80° C. oven for 4 h. The dried
product was heat treated at a temperature of 600° C. for 6 h,
repeating the process for 3 times to obtain a double core-shell
fluorescent material of Pt@SiO2@(Gd0.98,
Eu0.02)2O3.

Example 12

[0101] Preparation of the Au nano-particle sol: 4.12 mg of chloroauric
acid (H2AuCl6.6H2O) was dissolved into 8.4 ml of deionized
water. When the chloroauric acid was completely dissolved, 14 mg of
sodium citrate and 6 mg of cetyl trimethyl ammonium bromide were weighted
and dissolved in the chloroauric acid solution with magnetic stirring.
1.9 mg of sodium borohydride and 17.6 mg of ascorbic acid were dissolved
into 10 ml of deionized water respectively to prepare 10 ml of sodium
borohydride aqueous solution with the concentration of 5×10-3
mol/L and 10 ml of ascorbic acid aqueous solution with the concentration
of 1×10-2 mol/L. Under magnetic stirring, 0.04 ml of sodium
borohydride aqueous solution was added in drops into the chloroauric acid
solution, stirred for 5 min, 1.56 ml of ascorbic acid aqueous solution
with the concentration of 1×10-2 mol/L was then added in drops
into the chloroauric acid aqueous solution, continuing to react for 30
min to prepare 10 ml of Au nano-particle sol with a concentration of
1×10-3 mol/L. 10 mg of PVP was added into 6 ml of Au
nano-particle sol with magnetic stirring for 8 h to obtain a surface
treated Au nano-particle.

[0102] Preparation of Au@SiO2 microsphere and surface modification: 6 ml
of surface treated Au nano-particle is diluted with deionized water to 10
ml. Followed by adding 25 ml of anhydrous ethanol and 2 ml of ammonia
with magnetic stirring. 1 ml of TEOS is added in drops under stirring.
After the dropping, the mixture was stirred for 3 h to obtain an
Au@SiO2 microsphere suspension. The obtained Au@SiO2
microsphere suspension was centrifuged by a speed of 12000 rpm, washed
three times with deionized water, to remove the remaining ammonia and
residual TEOS, to obtain a purified Au@SiO2 microsphere. The
obtained Au@SiO2 microsphere was dispersed into deionized water via
ultrasonic to prepare 10 ml of Au@SiO2 suspension.

[0103] Preparation of Au@SiO2@(Gd0.95,
Eu0.05)2O3. 3.620 g of Gd2O3 and 0.1853 g of
Eu2O3 were weighted according to a molar ratio of
Gd(NO3)3 to Eu(NO3)3 of 0.95:0.05. Gd2O3
and Eu2O3 were dissolved with concentrated nitric acid to
prepare 15 ml of mixture solution containing Gd(NO3)3 and
Eu(NO3)3, in which the sum concentration of the Gd3+ and
Eu3+ is 0.71 mol/L. 85 ml of ethanol and 4.09 g citric acid were add
into nitrate mixture solution, after stirring, 8 g of PEG was added, the
solution was stirred in a 40° C. of water bath for 6 h in form a
sol. The prepared Au@SiO2 suspension was added into the sol, the
solution was stirred in a 70° C. of water bath for 8 h to form a
gel. The gel was dried in a 90° C. oven for 3 h. The dried product
was heat treated at a temperature of 800° C. for 5 h, repeating
the process for 3 times to obtain a double core-shell fluorescent
material of Au@SiO2@(Gd0.95, Eu0.05)2O3.

Example 13

[0104] Preparation of the Ag nano-particle sol: 3.40 mg of silver nitrate
(AgNO3) was dissolved into 18.4 ml of ethanol. When the silver
nitrate was completely dissolved, 42 mg of sodium citrate was weighted
and dissolved in the silver nitrate ethanol solution with magnetic
stirring. 5.7 mg of sodium borohydride was dissolved into 10 ml ethanol
to obtain 10 ml sodium borohydride ethanol solution with a concentration
of 1.5×10-2 mol/L. Under magnetic stirring, 1.6 ml of sodium
borohydride ethanol solution with a concentration of 1.5×10-2
mol/L was added to the silver nitrate ethanol solution, continuing to
react for 15 min to prepare 20 ml of Ag nano-particle sol with a
concentration of 1×10-3 mol/L. 40 mg of PVP was added into 8
ml of Ag nano-particle sol with magnetic stirring for 6 h to obtain a
surface treated Ag nano-particle.

[0105] Preparation of Ag@SiO2 microsphere and surface modification: 8
ml of surface treated Ag nano-particle is diluted with deionized water to
10 ml. Followed by adding 30 ml of anhydrous ethanol and 4 ml of ammonia
with magnetic stirring. 1.5 ml of TEOS is added in drops under stirring.
After the dropping, the mixture was stirred for 3 h to obtain an
Ag@SiO2 microsphere suspension. The obtained Au@SiO2
microsphere suspension was centrifuged by a speed of 12000 rpm, washed
three times with deionized water, to remove the remaining ammonia and
residual TEOS, to obtain a purified Ag@SiO2 microsphere. The
obtained Ag@SiO2 microsphere was dispersed into deionized water via
ultrasonic to prepare 15 ml of Ag@SiO2 suspension.

[0106] Preparation of Ag@SiO2@(Gd0.94,
Eu0.06)2O3. 2.748 g of Gd2O3 and 0.2253 g of
Eu2O3 were weighted according to a molar ratio of
Gd(NO3)3 to Eu(NO3)3 of 0.94:0.06. Gd2O3
and Eu2O3 were dissolved with concentrated nitric acid to
prepare 20 ml of mixture solution containing Gd(NO3)3 and
Eu(NO3)3, in which the sum concentration of the Gd3+ and
Eu3+ is 1.28 mol/L. 60 ml of ethanol and 9.84 g citric acid were add
into nitrate mixture solution, after stirring, 6 g of PEG was added, the
solution was stirred in a 50° C. of water bath for 5 h in form a
sol. The prepared Ag@SiO2 suspension was added into the sol, the
solution was stirred in an 80° C. of water bath for 5 h to form a
gel. The gel was dried in a 90° C. oven for 3 h. The dried product
was heat treated at a temperature of 900° C. for 4 h to obtain a
double core-shell fluorescent material of Ag@SiO2@(Gd0.94,
Eu0.06)2O3.

Example 14

[0107] Preparation of the Pd nano-particle sol: 0.43 mg of palladium
chloride (PdCl2.2H2O) was dissolved into 8.5 ml of deionized
water. When the palladium chloride was completely dissolved, 35.0 mg of
PVP was weighted and dissolved in the palladium chloride aqueous
solution. 3.8 mg of sodium borohydride was dissolved into 10 mL deionized
water to obtain 10 ml sodium borohydride aqueous solution with a
concentration of 1×10-2 mol/L. Under magnetic stirring, 0.48
ml of sodium borohydride aqueous solution with a concentration of
1×10-2 mol/L was added to the palladium chloride aqueous
solution, continuing to react for 20 min to prepare 10 ml of Pd
nano-particle sol with a concentration of 1×10-4 mol/L. 100 mg
of PVP was added into 10 ml of Pd nano-particle sol with magnetic
stirring for 4 h to obtain a surface treated Pd nano-particle.

[0108] Preparation of Pd@SiO2 microsphere and surface modification:
10 ml of surface treated Pd nano-particle was diluted with deionized
water to 20 ml. Followed by adding 50 ml of anhydrous ethanol and 7 ml of
ammonia with magnetic stirring. 3 ml of TEOS is added in drops under
stirring. After the dropping, the mixture was stirred for 6 h to obtain a
Pd@SiO2 microsphere suspension. The obtained Pd@SiO2
microsphere suspension was centrifuged by a speed of 12000 rpm, washed
three times with deionized water, to remove the remaining ammonia and
residual TEOS, to obtain a purified Pd@SiO2 microsphere. The
obtained Pd@SiO2 microsphere was dispersed into deionized water via
ultrasonic to prepare 20 ml of Pd@SiO2 suspension.

[0109] Preparation of Pd@SiO2@(Gd0.90,
Eu0.10)2O3. 6.102 g of Gd2O3 and 1.056 g of
Eu2O3 were weighted according to a molar ratio of
Gd(NO3)3 to Eu(NO3)3 of 0.90:0.10. Gd2O3
and Eu2O3 were dissolved with concentrated nitric acid to
prepare 15 ml of mixture solution containing Gd(NO3)3 and
Eu(NO3)3, in which the sum concentration of the Gd3+ and
Eu3+ is 2 mol/L. 45 ml of ethanol and 6.92 g citric acid were add
into nitrate mixture solution, after stirring, 12 g of PEG was added, the
solution was stirred in a 60° C. of water bath for 4 h in form a
sol. The prepared Pd@SiO2 suspension was added into the sol, the
solution was stirred in a 90° C. of water bath for 3 h to form a
gel. The gel was dried in a 100° C. oven for 2 h. The dried
product was heat treated at a temperature of 1000° C. for 2 h to
obtain a double core-shell fluorescent material of
Ag@SiO2@(Gd0.90, Eu0.10)2O3.

[0110] FIG. 2 shows an emission spectrum of the Au@SiO2@(Gd0.94,
Eu0.06)2O3 (11) according to example 1 comparing with a
conventional SiO2@(Gd0.94, Eu0.06)2O3 (12). As
shown in FIG. 2, the integral area of luminescence spectra 11 is 11.59
times of that of the luminescence spectra 12, which shows that the dual
core-shell fluorescent materials of Example 1 greatly enhance the
luminous intensity by the core metal gold particles. In addition, the
peak position of the luminescence spectra 11 and 12 are substantially the
same and between 600 nm to 650 nm, which means it irradiates red light.

[0111]FIG. 3 shows an emission spectrum of the
Pt@SiO2@(Gd0.999, Eu0.001)2O3 (21) according to
example 2 comparing with a conventional SiO2@(Gd0.999,
Eu0.001)2O3 (22). As shown in FIG. 3, the integral area of
luminescence spectra 21 is 6.47 times of that of the luminescence spectra
22, which shows that the dual core-shell fluorescent materials of Example
2 greatly enhance the luminous intensity by the core metal Pt particles.

[0112] FIG. 4 shows an emission spectrum of the Ag@SiO2@(Gd0.93,
Eu0.07)2O3 (31) according to example 3 comparing with a
conventional SiO2@(Gd0.999, Eu0.001)2O3 (32). As
shown in FIG. 4, the integral area of luminescence spectra 31 is 5.44
times of that of the luminescence spectra 32, which shows that the dual
core-shell fluorescent materials of Example 2 greatly enhance the
luminous intensity by the core metal Ag particles.

[0113] FIG. 5 shows a photoluminescence spectrum of the
Au@SiO2@(Gd0.95, Eu0.05)2O3 according to example
7 comparing with a conventional SiO2@(Gd0.95,
Eu0.05)2O3. The luminescence spectrums are arranged in an
order according the arrow, in other words, the higher luminescence
spectrum represents Au@SiO2@(Gd0.95, Eu0.05)2O3,
and the lower luminescence spectrum represents SiO2@(Gd0.95,
Eu0.05)2O3. As shown in FIG. 5, the integral area of
luminescence spectra of Example 7 is 1.73 times of that of the
conventional fluorescent material, which shows that, under a
light-induced condition, the dual core-shell fluorescent materials
greatly enhance the luminous intensity by the core metal gold particles,
thus facilitating the application in the product such as
photoluminescence device.

[0114]FIG. 6 shows a cathode ray luminescence spectrum of the
Au@SiO2@(Gd0.95, Eu0.05)2O3 according to example
7 comparing with a conventional SiO2@(Gd0.95,
Eu0.05)2O3. As shown in FIG. 6, the integral area of
luminescence spectra of Example 7 is 1.56 times of that of the
conventional fluorescent material, which shows that, under a cathode ray
excited condition, the dual core-shell fluorescent materials greatly
enhance the luminous intensity by the core metal gold particles, thus
facilitating the application in the product such as field emission
devices device.

[0115]FIG. 7 shows a photoluminescence spectrum of the
Ag@SiO2@(Gd0.94, Eu0.06)2O3 according to example
8 comparing with a conventional SiO2@(Gd0.94,
Eu0.06)2O3. As shown in FIG. 7, the integral area of
luminescence spectra of Example 8 is 1.48 times of that of the
conventional fluorescent material, which shows that, under a
light-induced condition, the dual core-shell fluorescent materials
greatly enhance the luminous intensity by the core metal Ag particles,
thus facilitating the application in the product such as
photoluminescence device.

[0116] FIG. 8 shows a cathode ray luminescence spectrum of the
Ag@SiO2@(Gd0.94, Eu0.06)2O3 according to example
8 comparing with a conventional SiO2@(Gd0.94,
Eu0.06)2O3. As shown in FIG. 8, the integral area of
luminescence spectra of Example 8 is 1.37 times of that of the
conventional fluorescent material, which shows that, under a cathode ray
excited condition, the dual core-shell fluorescent materials greatly
enhance the luminous intensity by the core metal Ag particles, thus
facilitating the application in the product such as field emission
devices device.

[0117]FIG. 9 shows a photoluminescence spectrum of the
Ag@SiO2@(Gd0.94, Eu0.06)2O3 according to example
13 comparing with a conventional SiO2@(Gd0.96,
Eu0.06)2O3. As shown in FIG. 9, the integral area of
luminescence spectra of Example 13 is 1.85 times of that of the
conventional fluorescent material, which shows that, under a
light-induced condition, the dual core-shell fluorescent materials
greatly enhance the luminous intensity by the core metal Ag particles,
thus facilitating the application in the product such as
photoluminescence device.

[0118]FIG. 10 shows a cathode ray luminescence spectrum of the
Ag@SiO2@(Gd0.94, Eu0.06)2O3 according to example
13 comparing with a conventional SiO2@(Gd0.94,
Eu0.06)2O3. As shown in FIG. 10, the integral area of
luminescence spectra of Example 13 is 1.34 times of that of the
conventional fluorescent material, which shows that, under a cathode ray
excited condition, the dual core-shell fluorescent materials greatly
enhance the luminous intensity by the core metal Ag particles, thus
facilitating the application in the product such as field emission
devices device.

[0119] In summary, according to FIG. 2 to FIG. 10, the double core-shell
fluorescent material according to the present disclosure exhibits a
greater luminous intensity. In addition, according to FIG. 5 to FIG. 10,
whether under photoluminescence or cathode excitation light-emitting
conditions, the double core-shell fluorescent material can also exhibit a
greater luminous intensity. The luminous conditions described above are
given only as an example, and the double core-shell fluorescent material
of the present invention is not limited to the above light emitting
devices in practical applications.

[0120] Furthermore, according to the Examples, the obtained double
core-shell fluorescent material is shaped as non-reunion or less reunion
spherical particle, which has a better application performance. The
particle size distribution uniformity and stability of the fluorescent
material is increased, such that the fluorescent materials exhibit a
uniform and stable luminous performance. Moreover, the amount of the
phosphor can be saved. Referring to the preparation method, the double
core-shell fluorescent material is obtained by sol-gel method or
precipitation method with two steps of coating, which is simple, easy to
control, and has a low cost, thus having broad prospects for production
applications.

[0121] Although the invention has been described in language specific to
structural features and/or methodological acts, it is to be understood
that the invention defined in the appended claims is not necessarily
limited to the specific features or acts described. Rather, the specific
features and acts are disclosed as sample forms of implementing the
claimed invention.